It has been the practice for many years to insert a cylindrical liner into a cylindrical automotive drive shaft for the purpose of damping vibrations and attenuating, at least to some extent, noise transmitted along the shaft. Examples of such liners are disclosed in U.S. Pat. Nos. 2,751,765; 4,014,184; 4,124,928; and 4,909,361.
Although the known liners have the capability of functioning satisfactorily, several factors may have an adverse effect on their efficiency. For example, the liners obviously must be manufactured prior to assembly with the drive shafts and often must be shipped from the point of manufacture to the point of assembly with the drive shafts. During the time between manufacture and assembly, the liners may be exposed to wide variations in humidity. If the liners are formed of paper, as is customary, and if the paper from which the liners are formed is hygroscopic, as conventionally is the case, humidity changes can and do affect some of the properties of the liners.
If a liner is formed of a cylindrical paper core having an exterior layer of corrugated material, such corrugated layer having alternating grooves and upstanding flutes, changes in humidity may cause considerable variations in the resistance to deformation of the flutes, as well as the spring rate or recovery characteristic of the flutes from such deformation. As a consequence, the force required to insert a liner into a drive shaft may vary considerably due to changes in humidity.
It is conventional to close the ends of a drive shaft following insertion of a liner into the shaft, thereby minimizing the effect of subsequent changes in humidity. Following insertion of the liner and closing the ends of the shaft, the shaft containing the liner is balanced. However, if the liner has shrunk radially due to a relatively low humidity at the time of insertion of the liner in its shaft, the position of the liner in the shaft may change in response to torsional forces to which the shaft is subjected following its inclusion in a vehicle. Relative movement between the liner and the shaft is objectionable because the shaft then may become unbalanced, thereby defeating the purposes for which the liner is incorporated in the shaft.
A liner constructed in accordance with the invention overcomes the disadvantages referred to above.